1. Field
The present disclosure relates generally to rock drilling units for drilling deep holes and the tensioning system on the chain drive for such drilling units.
2. Background
Some rock drills translate along a feed channel which supports the drill as the drill bit digs deeper within rocky earth or other material. The feed channel is tens of feet long. A drill bit is connected to the rock drill by one or more drill rods. When the rock drill is at the bottom of travel along the feed channel, the rock drill is pulled out and an additional drill rod is installed in between the drill bit and the rock drill. Drilling recommences with the rock drill at the end of the feed channel which is farther away from the hole being drilled. As drilling continues, the rock drill moves along the feed channel until it is once again at the bottom of travel.
The rock drill moves along the feed channel by a chain drive system. One end of a chain is connected to one end of the rock drill and the other end of the chain to the other end of the rock drill. The chain and rock drill form a loop which is looped over an idler sprocket coupled to one end of the feed channel and a tensioner sprocket at the other end of the feed channel. The chain further engages with a drive sprocket of a chain feed drive. The chain feed drive controls the movement of the rock drill along the feed channel as well as providing a force on the rock drill in the direction of the drill bit, i.e., to provide force on the drill bit to facilitate the drill bit in grabbing onto the material into which a hole is being drilled.
Proper operation of the chain drive system is ensured by maintaining a specified chain tension in the chain so that the chain does not jump teeth of the sprockets and by replacing the chain when it has stretched beyond a predetermined amount. In some systems, the tension is adjusted manually prior to putting the drill unit in service for a shift. Although such practice is desirable, not all drill operators remember to perform such maintenance regularly. Furthermore, in a situation where the drill unit is operated continuously for long periods of time, the chain may stretch sufficiently since the last adjustment so that the chain jumps a tooth during a single shift. Damage to the sprocket and surrounding hardware can occur in a single instance of the chain jumping off the sprocket. Once the chain jumps a first time, it is likely to regularly jump off the sprocket because the tension in the chain is insufficient to hold the chain within teeth of the sprocket.
Another maintenance issue associated with such rock drills is in providing an indication of when chain replacement is recommended.